1. Field of the Invention
The present invention relates to a drive apparatus for a brushless DC motor mounted on, e.g., a compressor, and a failure diagnosing method for diagnosing whether a failure occurs in the brushless DC motor and the drive apparatus.
2. Description of the Related Art
A brushless DC motor is constituted by a stator on which a plurality of phase coils are mounted, and a rotor provided with permanent magnets.
A drive apparatus for this brushless DC motor is constituted by an inverter for rectifying a voltage from an AC power supply, converting the voltage to an AC voltage having an arbitrary frequency, and outputting the obtained AC voltage, a position detection circuit for detecting a rotational position of the rotor of the brushless DC motor, and a controller for turning on/off the respective switching elements of the inverter in accordance with the detection result obtained by the position detection circuit.
The inverter is constituted by a DC voltage circuit for rectifying the AC voltage from the AC power supply and outputting an obtained DC voltage, and a plurality of switching elements to which the output voltage from the DC voltage circuit is applied.
When the switching elements of the inverter are turned on/off, a current sequentially flows to the respective phase coils of the brushless DC motor. When power is supplied to the phase coils, the respective phase coils generate magnetic fields. The rotor is rotated by the interaction of the magnetic fields of the phase coils and the magnetic fields of the permanent magnets of the rotor. Switching of power supply to the respective phase coils is called commutation.
When the rotor is rotated, a voltage is induced in one phase coil to which power is not supplied. The induced voltage is input to the position detection circuit. The position detection circuit compares the input induced voltage with a predetermined reference voltage. When the level of the induced voltage and the level of the reference voltage intersect, the position detection circuit outputs a reference position detection signal. The reference position detection signal is input to the controller.
The controller determines the commutation timing in response to input of the reference position detection signal. Rotor position detection and commutation are repeated in this manner, thereby continuing rotation of the rotor.
The drive apparatus and the brushless DC motor are electrically connected to each other through a connector. This connector comprises a drive apparatus-side terminal and a motor-side terminal. The two terminals of this connector are connected by a manual operation upon shipping from the manufacturer.
If a trouble occurs in the operation of the brushless DC motor, the person in charge of maintenance disconnects the two terminals of the connector to determine whether the cause of the trouble exists in the drive apparatus or in the motor.
When, however, the two terminals of the connector are disconnected, the voltage induced in the phase coil to which power is not supplied cannot be fetched by the position detection circuit. In other words, the position of the rotor cannot be detected. Then, the inverter cannot be started, making it difficult to determine the cause of the trouble.